Data storage devices for use in computers and the like have, over the years, taken on many forms. Some of the earliest devices used to store data have included magnetic core storage, acoustical delay lines, flip-flops and the like. As semiconductor technology developed, however, semiconductor based storage devices came to be the most common form of data storage device for direct high speed access by computers and other electronic devices requiring high speed data storage.
The needs for data storage devices in electronic computers and other electronic devices seems to be insatiable. Every year, engineers seek to have greater and greater storage devices available. One of the most widely used storage device today is the DRAM (dynamic random access memory) device. Another frequently used storage device is the SRAM (static random access memory) device. These devices usually take the form of a plurality of storage cells arranged in a regular grid pattern on a semiconductor substrate.
As the size of transistors has become smaller, the number of storage locations in each such device has risen with the capacity going up 4 times the capacity of the next earlier generation of storage device. At the present time, devices having a capacity of 64 million bits are being developed while devices with even greater capacity are being contemplated. During the development phase of devices of this and larger capacity, developers increasingly realize that the smaller geometries of semiconductor devices provides significant engineering barriers that have to be overcome before the new product can be manufactured. Indeed, it is generally believed that radically new designs may be needed to meet storage density requirements of the future and that simply making existing designs smaller will not always be a workable plan for future.